The title of this short story "The Necklace" represents the materialism that misguides Mathilde the main character and it is the focal point of the story.
Mathilde is unhappy with her rank in society and also with her husband "a little clerk at the Ministry of Public Instruction". Although, she enjoys of a middle class social status, she is sick of it. Mathilde is "feeling herself born for all the delicacies and all the luxuries".
The necklace is a symbol of the expensive things that she dreams about in vain. At first sight of this jewel "her heart began to beat covetously". This euphoria reveals her greed, she probably imagines herself wearing it and making all the women envious at the party. Yes, Mathilde wants to be wealthy, and she desires this necklace badly so that she can pretend for one night to be part of a more fortunate class of people.
However, the necklace is far of making Mathilde happy, her satisfaction is temporary. For one night of being accepted among rich people she had to suffer ten years of debts. Maupassant foreshadows a terrible calamity: at that point when the party was over "All was ended, for her". This is a gloomy and upsetting story, and one of the lessons is that paying exaggerated attention to material things is more damaging than helpful. In Chile people say that misfortune reigns in somebody else's belongings, and this is another lesson of the story. .
The secret of life is being happy with many materials possession, but also being happy with the minimum. Mathilde showed herself responsible for the lost necklace, but perhaps things could have been different for her if she had appreciated the life she had together with her husband, her real treasure. .